Much of the fighting in World War I took place along the Western Front, within a system of opposing manned trenches and fortifications (separated by a "no man's land") running from the North Sea to the border of Switzerland. On the Eastern Front, the vast eastern plains and limited rail network prevented a trench warfare stalemate from developing, although the scale of the conflict was just as large. Hostilities also occurred on and under the sea and — for the first time — in the air. More than nine million soldiers died on the various battlefields, and millions more civilians perished.

The war caused the disintegration of four empires: the Austro-Hungarian, German, Ottoman, and Russian. Germany lost its overseas empire, and states such as Czechoslovakia and Yugoslavia were created, or recreated, as in the cases of Lithuania and Poland. This contributed to a decisive break with the world order that had emerged after the Napoleonic Wars, which was modified by the mid-19th century’s nationalistic revolutions. The results of World War I would also be important factors in the development of World War II just over two decades later.

The battle of the Marne was a major turning point of World War I. By the end of August 1914, the whole Allied army on the Western Front had been forced into a general retreat back towards Paris. Meanwhile the two main German armies continued through France. It seemed that Paris would be taken as both the French and the British fell back towards the Marne River.

He was chosen as supreme commander of the allied armies during World War I, on March 26, 1918, five days after the start of the Spring Offensive, the final attempt by Germany to win the war. He served until November 11, 1918, when he accepted the German Surrender.

He advocated harsh peace terms that would make Germany unable to ever pose a threat to France again. His word after the Treaty of Versailles, “This is not a peace. It is an armistice for 20 years”, would prove prophetic.